Process for the production of chlorine dioxide



April 20, 1937. G. P. VINCENT 2,078,045

PROCESS FOR THE PRODUCTION OF CHLORINE DIOXIDE Filed June 1'?, 1956 3 ShQets-Sheet 1 INVENTOR u @ewige ZID/0766225 PROCESS FOR THE PRODUCTION OF CHLORINE DIOXIDE gwdg/www@ TTORNEYS April 20, 1937. G. P. VINCENT PROCESS FOR THE PRODUCTION OF CHLORINE DIOXIDE Filed June 1'7, 1936 3 Sheets-Sheet 3 Patented; Api; zo, 1931 2,078,045

UNITED STATES PATENT OFFICE Pnoclzss Fon 'ma PnonUc'rroN -or cnLomNE moxmr:

George Paul Vincent, New York, N.' Y., assilgnor to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia' Application .lune 17, 1936, Serial No. 85,666

4 claims. (cl. 23T-152) This invention relates to improvements in the' ing 45-75 C. forv example. The acid reaction, production of chlorine dioxide. More. particuthe second step, is with advantage, however, carlarly, the invention provides an improved operaried out as described in my applications filed tion embodying a special calcium cycle for the June 1'?, 1936, Serial Numbers 85,667 and 85,668.

2* production of chlorine dioxide from chlorine, The acid reaction may be carried out as a' conlimeand hydrochloric acid. tinuous operation or as a succession o'f batch op- The operation o'f the invention consists essenerations.' In batch operation, the Vacid concentially of a special combination of three steps, tration is with advantage limited: at the begin' first, the formation of calcium chlorate by furs ning of the operation and increased as the relu ther chlorination of partially chlorinated lime, action proceeds to promotecomplete-decomposilo second, the liberation of a gas mixture includtion of the calcium chlorate, If sulphuric acid ing chlorine .and chlorine dioxide by reacting .is used in either type 'of operation, the acid the thus formed calcium chlorate with hydr-oshould be supplied to the reaction at a rate low .chloric acid, andthird, the separation of chlorine enough to avoid caking of the calcium sulphate l5 from this 4gas mixture by selective absorption by formed and the total proportion'of acid supplied l lime', ,the partially chlorinated lime formed in tothe reaction-may with advantage approximate the third step being supplied to the first step 4-or 5 timesthat required to completely decomto complete the calcium cycle. In the combined pose the calcium chlorate. The separation of operation of the invention, the clorination to chlorine from the gas mixture including chlorine forml calcium chlorate, the r'st step, is eiected and chlorine dioxide formed in the secondstep 2'() in the presence of sufficient water to dissolve the may with advantage be effected as described in calcium chlorate and at least part of the calan application led August 15, 1934, by James cium chloride formed to form a calcium chlorate F. White, Serial'Number 739,938, or as described liquor Vto be supplied to the acid reaction, the in an application filed.l by me August .15, 1934, g5 second step. The acid reaction, the second step, Serial Number 739,941, using calcium hydroxide 25 is carried out without requiring removal of such as the separating reagent. For example, the gas calcium chloride. V mixture including chlorine andlchlorine dioxide Hydrochloric acid is, with advantage, supplied is passed in contact with a quantityof dry 'or to the second step as such. It may, however, substantially drycalcium. hydroxide ysubstan- :zo subject to disadvantages involved in the'relative tially exceeding that required to react with all 30,

insolubiiity of calcium sulphate, be generated in of the chlorine present. A proportion of lime the second step by reaction between the calcium such that it is not more than chlorinated chloride present and sulphuric acid supplied to is advantageous. In the combined operation of the second step. The combined operation of the this invention, the lime, and with advantage all :s3 invention includes, in connection with the use of of the lime, supplied to the rsut step is used as 35 suiphuric acid in the second step, a subordinate the separating reagent in the third step, prosulphuric acid cycle. When using sulphuric acid viding an appropriate excess promoting the efin the operation of the invention, the'calcium fective separation of chlorine fromjthe gas mixof calcium chlorate and calcium chloride enterture and at the same time being partially chlo- 40 ing the conversion reaction becomes calci-um sulrinated thus improving the overall efficiency of 40 phate. In one embodiment of the invention, the combined operation. This separation may such calcium sulphate is separated from the be carried out at temperatures approximating reaction liquor making possible the return of the atmospheric temperatures and, in general, any reaction liquor to the sulphuric acid reaction, provision for supplying heat to or carrying off after calcium sulphate separation and approheat formed in the reaction is unnecessary. 45 priate concentration. The accompanying ilow diagrams, Figs. 1 and 'I'he precise manner in which the several steps 2 of the drawings, will further illustrate the inmaking up the combined operation oi the invention. vention are carried out is not essential to the That portion of the flow diagram Fig. 1 in solid present invention. For example, except for the lines represents, for example, an operation such 50 supplying oi.' partially chlorinated lime to the as that of the rst of the following examples.. In iirst step, this step may be carried out in accordthe chlorinator l partially chlorinated lime from ance with conventional practice for the producthe separator 3 is chlorinated to form calcium tion of calcium chlorate, by effecting the chlorichlorate. In the generator 2 the calcium chlonation at an elevated temperature, approximatratecalcium chloride liquor initially formed in 55 chlorine dioxide.l

an aqueous slurry of caustic soda, lime andI petroleum coke in the absorber 9 to form an aqueous solution of sodium chlorite. which is separated from .the suspended solids in filter IB and thereafter dried in the drier. I I to produce a solid sodium chlorite product.

That portion of thefiow diagram Fig. 2in solid lines-represents, for example, an operation such as that of thesecond of the following examples. In the chlorinator Ia partially. chlorinated lime from the separator 3a. is chlorinated to form calcium chlorate. In the generator 2a the calcium chlorate-calcium chloridel liquor initially formed in the chlorinator I a is reacted with sulphuric acid to liberate a gas mixture including chlorine and chlorine dioxide. The chlorine content of this gas mixture is separated in theseparator 3a in the partial chlorination of the lime supplied from the separator 3a to the chlorinator la'. After concentration in the evaporator 4a, calcium chloride is precipitated in the crystallizer 5a from the calcium chlorate-calcium chloride liquor from the chlorinator la. This precipitated calcium chloride isseparated from the calcium chlorate-calcium chloride liquor inthe centrifuge 6a. precipitated calcium 'sulphate is separated in the centrifuge 'Ia from 40 the reaction liquor from the. generator 2a. After this separation of calcium sulphate, the reaction liquor is concentrated in evaporator 8a and, together with fresh sulphuric acid, returned to the generator 2a. The chlorine dioxide component of the gas mixture from the separator 3a is absorbed in an aqueous slurry of caustic soda, lime and petroleum coke, to produce a solid sodium chlorite productas-described in connection with Fig. 1.

The reaction liquor from the generator 2a after being separated from the precipitated calcium sulphate in the centrifuge 'la may be supplied, as described above, directly to the evaporator 8a, or, as in an operation such as that of the third of the foregoing examples, may be delivered to chlorine which is supplied to the chlorinator Ia,

and avcalcium chloride solution containing a small amount of precipitated calcium sulphate.

This solution is supplied directly to the evapo-- rator 8a. The reaction liquor from the generator 2a. may likewise be subjected to treatment with steam in the still I2a, thus yielding chlorine and a calcium chloride solution containing a considerable amount of precipitated calcium sulphate. The'precipitated calcium sulphate is separated from the calcium chloride liquor in centrifuge I3a and the clear liquor then supplied to the evaporator 8a.- The reaction liquor from the generator 2a may also be supplied to the still I2a and the total content of calcium sulphate separated in centrifuge I3a.

The invention will be further illustrated by the following example of a particularly advantageous The chlorine dioxide component of the operation embodying the invention, appropriate apparatus for carrying this operation being il-l lustrated, diagrammatically and conventionally, in Figure 3 of the accompanying drawings: Lime is supplied to the separator 3', a-rotating cylinder provided internally with lifts to shower the lime through the gas stream flowing through the separator, at a rate of 117.5 pounds per hour Ca(OI -I),2, and in the separator is about 25% chlorinated. A slurry formed by the addition of water at a rate of 35 gallons per hour to this partially chlorinated lime in tank 4 is chlorinated, in the tile packed towers I' and' 5, at a temperature approximating 50-80 C., with chlorine supplied through connection 6 at a 'rate of 84 pounds per hour. Of this chlorine, about 62 parts are supplied as make-up chlorine through connection I 'and about 22 parts are supplied as recovered end of the generator 2', from tank I0', at a rate of 18 gallons per hour, this total quantity being divided'between the upper two or upper three chambers in the generator. Air is forced into the lower end of the generator by means of blower II'fat a rate oi' 40 cu. ft. per minute. With a generator consisting of 9 chambers each retaining 19 gallons, the reaction time in the generator approximates 3.8 hours. With a reaction temperature of 2030 C., about 78.4% of the calcium chlorate is decomposed. Chlorine-dioxide is produced at a rate of about 21.7 pounds per hour and chlorine at a rate of about 22.8 pounds per hour, this mixture of chlorine dioxide and chlorine, diluted with air, passing from the generator 2 to the separator 3' through duct I2. In the separator 3' the chlorine content of this gas mixture is selectively absorbed in partially chlorinating the-lime, thus producing the partial- 1y chlorinated lime supplied to the chlorination effected in the tower I', and in the tower 5, and a mixture of chlorine dioxide in air containing about 5% by volume of C102, this chlorine dioxide mixture being discharged through' duct I3. 'Ihe chlorine dioxide component of the gas mixture discharged through duct I3 may be used to produce sodium chlorite.

The residual liquor from the reaction between the chloride-chlorate liquor and the hydrochloric acid, discharged from the generator 2' through connection I4, is introduced into the upper end of the recovery tower I5, a tile packed tower. Steam is blown into the pot I 6' connected to the lower end of the tower I'I at a rate.l

suillcient to heat the liquor entering the pot to boiling. The evolved vapor mixture, steam, chlorine and chlorine dioxide, passes up through the tower I5 in countercurrent to thecooler residual liquor from the generator. The thus re,

covered chlorine, and chlorine dioxide, pass .to

ing theinvention, this operation involving the steps for the ultimate lproduction of sodium chlorite from the chlorine dioxide produced: About 42.1 parts (by weight) of a partially chlorinated lime, formed by chlorination of 35.7 parts of 96% Ca(OH)2 are further chlorinated with 26 parts of chlorine-in the presence of 114 parts of water at a temperature of about 60 C. About 91.25 parts of water are evaporated, from the resulting lit uor, the vconcentrated liquor is cooled to about 30 C., and about 43.5 parts of precipitated calcium chloride tetrahydrate are separated from the cooled concentrated liquor. .The resulting calcium chloratecalcium chloride liquor, diluted with about 42.55 parts of water, is reacted with about 114 parts of 19 normal sulphuric acid. T he sulphuric acid may be supplied to the reaction mixture, for example, at a rate oi about 1 part per minute. Or, in batch operation, to improve the uniformity of the rate of liberation of chlorine dioxide, in amounts corresponding to 3.14 parts per minute for the iirst 5 minutes, none for the 6th to 8th minutes, in amounts corresponding to 1.14 parts per minute for the 9th to V43rd minutes, 2.07 parts per minute from the 44th to 49th minutes, 1.38 parts per minute for the 50th to 58th minute, 3.14 parts per minute for the 59th to 67th minutes and the balance during the 68th minute. The reaction mixture is vigorously agitated throughout the reaction and air is passed through the reaction vessel, at an initial rate of about 3.98 cubic feet per minute per pound of calcium chlorate supplied to 'the reaction and at a gradually reduced rate as `the reaction proceeds. The liberated chlorine and chlorine dioxide, diluted with air, are contacted with about 35.7 parts of 96% Ca(OH)z. The chlorine present is absorbed from the chlorine dioxide gas mixture by the lime. The thus partially chlorinated lime is supplied to the first-mentionedv chlorination. Precipitated calciumV sulphate, about 38 parts, is separated from the reaction liquor and washed with about 163 parts of water. The reaction liquor, from which calcium sulphate has been separated, combined with the wash liquor, approximately 6.5 normal with respect to sulphuric acid, is concentrated to a normality of about 15 by evaporation of 184.5 parts of water. About 27.4 parts of fresh sulphuric acid, H2SO4, is added to this thus concentrated acid, about 86.6 parts, and this acid mixture is supplied to the sulphuric acid reaction. The chlorine dioxide gas mixture, from which chlorine has been separated, including about 8.7 parts of chlorine dioxide, is scrubbed with an aqueous slurry 0.1 molar with respect to sodium hydroxide and containing 5 parts of calcium hydroxide and 5 parts of finely pulverized petroleum coke per parts of water. The concentration of sodium hydroxide, calcium hydroxide and coke is maintained by regular additions as the scrubbing is continued. The scrubbing medium is used until it is about 1.5 molar with respect to sodium chlorite. Suspended solids are then separated from the scrubbing medium, and the resulting sodium chlorite liquor is spray-dried or concentrated and then spray-dried to produce about 10 parts of sodium chlorite containing about 0.7 part of sodium chloride. The separated solids are resuspended in water, with appropriate additions, and re-used as a scrubbing medium until the calcium carbonate concentration of the thus formed scrubbing medium approximates 50 parts per 100 parts of Water when the separated solids are discarded.

-The invention will be further illustrated by the following example of another operation embodyuse of a calcium chloride-calcium chlorate liquor having a chloride-chlorate ratio of 5:1 and a smaller quantity of excess sulphuric acid than that used in the preceding example: Partially chlorinated lime, formed by chlorination of 47.8 parts of 96% Ca(OH)2 and containing 8.55 parts of chlorine, is further chlorinated by the addition of 124.05 parts of water and 35.4 parts of chlorine. After chlorination this liquor contains about 20.42 parts of calcium chlorate, 53.9 parts of calcium chloride and 135.2 parts of water. The resulting calcium chlorate-calcium chloride liquor is reacted with about 44.7 parts of 59% sulphuric acid added at the rate of .745 part per minute in batch operation. As a result of this reaction, 9.55 parts of chlorine dioxide and 8.55 parts of chlorine are evolved and are contacted with about 47.8 parts of 96% Ca(OH)2. The chlorine is absorbed by the lime and, as described in the preceding example, the thus partially chlorinated lime is supplied to the first-mentioned chlorination and practically all of the 9.55 parts of chlorine dioxide are subsequently reduced and absorbed in the aqueous caustic soda-lime-colre slurry. The liquid and solid, discharged from the reaction between the chloridechlorate liquor and the sulphuric acid, are separated and the clear liquor is then subjected to the action of steam. In this manner, the calcium chlorate remaining in the discharged liquid is decomposed yielding 5.49 parts of chlorine which are supplied to the first-mentioned chlorination. The 33.8 parts of calcium chloride resulting from this decomposition of the liquor with steam may be recovered in any suitable manner.

Chlorine dioxide produced in accordance with the invention may, of course, be used for the production of calcium chlorite or for any appropriate purpose such as the production of sodium chlorite, the ultimate product to which the last two ci the foregoing examples and the accompanying flow diagrams more particularly refer. For example, chlorites of the alkali metals and the alkaline earth metals may be produced from chlorine dioxide gas mixtures produced in accordance with this invention by absorption in an aqueous solution or suspension of the corresponding hydroxide in the presence of an appropriate reducing agent. Petroleum coke and sulphur dioxide, for example, may be used as reducing agents in this connection. In the production of sodium chlorite, the chlorine dioxide, or the chlorine dioxideair mixture, is with advantage scrubbed with an aqueous solution of caustic soda from 0.01 to 3.0 normal with respect to- NaOH and containing between about 0.5 and 100 grams per liter oi calcium hydroxide and from about 0.5 to 250 grams per liter of finely pulverized petroleum coke at a temperature in the range 0-100 C. To avoid discoloration of the sodium chlorite product, the concentration of the solution with respect to caustic soda is with advantage limited not to exceed about 1 molar, or better 0.5 molar. The concentration efficiency is improved by using the scrubbing Ine-- dium only until the concentration of the scrubbing medium With respect to sodium chlorite approximates 3 molar, or better 1 molar. The solids separated from this sodium chlorite liquor may be re-used, with appropriate additions of Water, carbon, lime and sodium hydroxide, as the scrubbing medium until the calcium carbonate content of the thus formed scrubbing medium approximates 750 grams, or better grams, per liter. When this concentration is reached, the separated solids taining some lime, may be supplied to the chlorination to form calcium chlorate as part of the 5 lime to be supplied to this reaction. When this,

calcium carbonatelime mixture is so used, however, it should be supplied directly to the chlorinatlon rather than to the chlorine separation, the third step of the combined operation of the l invention.

I claim:

1. In the production o! chlorine dioxide, the improvement which comprises separating chlorine from a gas mixture including chlorine and l chlorine dioxide by selective absorption of the chlorine by lime, subjecting the thus partially chlorinated lime to further chlorination` to form calcium chlorate, reacting the thus formed calcium chlorate with hydrochloric acid to liberate 20 a gas mixture including chlorine and chlorine dioxide, supplying this gas mixture'to the rstmentioned separation and taking oil.' chlorine dioxide from the ilrst-mentioned separation.

2. In the production of chlorine dioxide, the

25 improvement which comprises separating chlorine from a gas mixture including chlorine and chlorine dioxide by selective absorption of the' chlorine by lime, subjecting the thus partially chlorinated lime to further chlorination to form 30 calcium chlorate in the presence of suilicient water to dissolve the calcium chlorate formed, reacting the thus formed calcium chlorate liquor with hydrochloric acid to liberate a gas mixture including chlorine and chlorine' dioxide, supply- 35 ing this gas mixture to the rst-mentioned sepa- 3. In the production of chlorine dioxide, the improvement which vcomprises separating chlorine .from a gas mixture including chlorine and chlorine dioxide by selective absorption of the chlorine by lime, subjecting the thus partially chlo- -rinated lime tofurther chlorination to form calcium chlorate in the presence of sumcient water to dissolve the calcium chlorateand at least part of the calcium chloride formed, reacting the.

thus formed calcium chlorate-calcium chloride liquor with an acid to liberate a gas mixture including chlorine and chlorine dioxide, supplying thisgas mixture to the iirst-mentioned separation and taking oil chlorine dioxide from the first-mentioned separation.

4. In the production of chlorine dioxide, the improvement which comprises separating chlorine from a gas mixture including chlorine and chlorine dioxide by selective absorption of the chlorine by lime, subjecting the thus partially chlorinated Jlime to further chlorination to form calcium/chloe rate in the presence of sufcient water to dissolve the calcium chlorate and at least part of the calcium chloride formed, reacting the thus formed calcium chlorate liquor with sulphuric acid to liberate a gas mixture including chlorine and chlorine dioxide, supplying this gas mixture to the first-mentionedv separation, separating calciumsulphate from the liquor resulting from the sulphuric acid reaction and concentrating and returning the reaction liquor remaining after this calcium sulphateseparation to the sulphuric acid, and taking oi chlorine dioxide from the rstmentioned separation.

` GEORGE PAUL VINCENT.

first-mentioned separation. 

